Upgrade Joda Time to 1.6.2

Joda Time version 2.1 was released on 2012-02-22. According to the release notes and website, 2.0 was largely binary and source compatible with 1.6 (see the upgrade guide), so hopefully this is straightforward.

However, JBoss AS 7.1.1.Final uses version 1.6.2 (see here), so we should instead use that. We don't need any of the new features/capabilities in 2.0, but AS7 compatibility is far more important.